(1) Field of the Invention
The present invention relates to a removable air mandrel for use in positioning hydrophone groups in the fabrication of fiber optic towed array sonar systems and to a process for installing hydrophone mandrels into an array forming part of a sonar system.
(2) Description of the Prior Art
Inflatable mandrels have been used in a wide variety of technologies. For example, U.S. Pat. No. 3,425,642 to May illustrates an inflatable mandrel that transmits torque and radial lift to a winding roll by substantially increasing its diametrical load-carrying dimensions when inflated. The inflatable mandrel has a plurality of axially-spaced circumferentially extending tubes on a small diameter aluminum mandrel core and means for inflating the tubes so that the tubes expand radially away from the mandrel core to provide a cylindrical load-bearing surface having an outside diameter greater than the diameter of the mandrel core.
U.S. Pat. No. 4,144,632 to Stroupe exemplifies a method of making a tortuously shaped article wherein an inflatable mandrel is used as part of a single step low pressure operation. U.S. Pat. No. 4,632,328 to Bishop et al. illustrates yet another use for an inflatable mandrel. In the Bishop et al. patent, an air mandrel is described which is suitable for engaging a surface of a cylindrical object and transmitting torque and/or lifting pressure between the surface of the cylindrical object and a second concentrically figured cylindrical object also engaged by the mandrel.
U.S. Pat. No. 4,979,278 to Thompson relates to a device for axially and externally mounting an expandable sleeve onto, and dismounting the sleeve from, a cylinder. The diameter of the expandable sleeve is expanded by introducing a fluid capable of expanding the sleeve between the inner surface of the sleeve and the outer surface of the cylinder. The sleeve is contractable by the removal of the fluid.
Mandrels have also been used in the fabrication of optical fiber sensors and hydrophones. U.S. Pat. No. 5,256,237 to Maas et al. relates to a process for affixing wound optical fibers on the inner surface of a hollow cylinder. The process requires that the fibers be supported on a cylinder, coated with an adhesive and placed within the sensor mandrel cylinder, at which time the circumference of the supporting cylinder is expanded, causing the fibers to engage the inner surface of the sensor mandrel cylinder. The adhesive is then cured, holding the fibers in place on the inner surface of the sensor mandrel cylinder while the supporting cylinder is contracted and removed from the sensor mandrel cylinder.
U.S. Pat. No. 5,317,544 to Maas et al. relates to a multiple segment fiber optic hydrophone which includes a plurality of hydrophone components separated by finite spacings and interconnected to provide a single output signal. Each hydrophone component is based upon a single-mandrel design in which a cylindrical body is apportioned into sensing and reference sections. The sensing sections comprise coaxial arrangements of pliant inner and outer cylinders separated by an annular airspace while the adjacent reference sections comprise solid-walled cylinders. Finite separation distances between the hydrophone components result in reduced flow noise occasioned by increased sensing area while detection sensitivity is maintained.
Sonar based systems for detecting underwater hazards and threats employ pressure-activated transducers of the hydrophone type to generate signals indicative of the presence and location of underwater objects. In use, a sonar system utilizes a predetermined arrangement of acoustic hydrophones to collect a spatial distribution of "echo" data that can be analyzed for information such as position and closing rate. The array is housed within a hose-like element that is fixed to an end of a towing cable.
Automated winding equipment has been developed for constructing fiber optic hydrophones on long continuous mandrels. Groups of short mandrels present a problem for this type of equipment because they are simply too short to be wound by themselves and there is a need to hold various hydrophones in a predetermined spatial relationship.
Key to producing low cost fiber optic hydrophones arrays is the ability to use automated winding equipment where at one end there is a supply reel of raw material and at the other end a reel of finished product.